Wet beneficiating of phosphate ores



July 30, 1963 Filed Aug. 31, 1960 H. W. ADAM WET BENEFICIATING OF' PHOSPHATE GRES 2 Sheets-Sheet 1 United States Patent C tion of New York Filed Aug. 31, 1960, Ser. No. 53,133 14 Claims. (Cl. 209-12) This invention relates to the beneciation of phosphate ores. More particularly, the invention relates to a process for the wet concentration of unsized phosphate minerals pursuant to which a substantial portion of the phosphate values of the ore are recovered.

Wet beneiiciation of phosphate ores has long been a common expedient Widely practiced in the industry. Ore ground to substantial liberation of its mineral values for example, to -14 mesh conventionally is sized by means of classifiers, screens, trommels, hydroseparators and the like to provide a -14 +35 fraction and -35 +150 or 200 mesh fraction. The coarser fraction, generally considered to be too coarse for froth flotation, is beneiiciated by means of spirals, shaking tables and the like. The liner -35 mesh fraction is subjected to froth flotation.

Early practice in .the concentration of phosphate ores comprising apatite or fluorapatite and a siliceous gangue entailed reagentizing the libenated nely divided ore with an` anionic reagent effective selectively to coat at least a portion of the surfaces of the phosphatic particles present, followed by concentration of the reagentized ore by froth flotation to provide a phosphate concentnate as a froth product and a silica tail as a depressed or sink product. At acceptable levels of recovery, particularly from relatively low-grade ores, the grade of the concentrates` was objeotionably low.

An alternative procedure known to the early art embraced` reagentizing the liberated phosphate ore with a cationic reagent effective selectively to coat at least a. por-tion of the surfaces of the silica particles, followed by froth otation .to produce a silica. tail as a froth product and a phosphate concentrate depressed or sink product. Such a. procedure likewise failed to afford a concentrate ofl satisfactory grade and recovery.

The Florida phosphate industry, in particular, accordingly resorted to a combined process pursuant toY whichv (l)k :the liberated phosphate ores are subjected to a first state of wet beneficiation in the presence of an anionic reagent` to produce a rougher concentrate comprised of reagent-bearing phosphatic minerals and a substantial amount of silica, (2) the rougher concentrate is treatedwith a mineral acid to remove the reagent coating, and` (3') the essentially reagent-free rougher concentrate is subjected to a second stage wet concentrationin the. presence of a cationic reagent effective to coat selectively the silica particles to produce a -inal phosphatecom centrate and reagentebearingwsilica tail. The combined process is described in detail in CragoPatent 2,293,640. Modifications of the Crago process which treat ii-nely divided ore `and embrace the same general sequence. of steps are describedfin. a-plur-ality of subsequentlyeissued patentsy including: Duke 2,461,813; Duke 2,661,842; Houston 2,706,558; Hunter 2,750,036.;` andV Duke 2,753,997. Reference is made .to the disclosuresI of eachl ofthe aforementionedpatents for a more detailed" teaching in respect to the concentration of phosphatic minerals withnanionic and cationic reagents, and methods knownl to the art forthe removal of suchreagentsfrom the concentrates produced. Significantly, each of they abovepatents sizes the phosphate feedl to obtain a -3'5- mesh feedwhich is subjected to the flotation process. Further,

each ,ofthe above patents,describesaprocess wherein only4 3,099,620 Patented. Ju-ly- 30, 1963 lCe the froth concentrate from. the anionic otation is subjectedv to further processing.

Further. modifications of the Crago process are exemplified by Duke Patent 2,676,705. In this instance phosphate ore is sized. to obtain a coarser fraction and a finer fraction, each ofv saidffractions being subjected [to an anionic notation. Again, however,r the underflow from. the anionic iiotation is discarded as siliceous waste.

Processes, such as the above, must rely on an accurate sizing of the liberated `loreto achieve efficient separation. In practice, however, it is extremely diicult to achieve an `accunatesizing of the ore. As a threshold matter, much yof the ground ore is characterized by a size ofy about y35 mesh. Moreover, `variations in the shape and speciiic gravity of the particles and their tendency to blind screens further contribute to an inaccurate sizing and ultimately to a lower recovery of the phosphate values of the ore.

Typical screen sizings of a liberated phosphate ore are as follows:

Coarse frac- Fine fraction, percent vtion, percent y i Mesh size It will be apparent. that such processing, requiring extensive sizing equipment, does not provide an eflicientv sizingv of the ore.

It is a primary object of this-invention to provide a method for the wet beneiiciation of phosphate ores pursuant to which high recoveries of phosphate values arerealized.

It is another object ofv this invention to provide a method for the. lwet beneficiation. of unsized phosphate ores pursuant to which a high proportion of the phosphate values are recovered.

It is a further object of this invention to provide a method for the wet beneiiciation of phosphate ores whichl does not require that the entire yground ore be subjectedto a. preliminary sizing;

In accordance with this invention there is provided a method of beneiiciating unsized phosphate ore which comprises:

v (1) Subjecting unsized liberated phosphate ore to froth flotation in the presence of an lanionic flotation reagent to provide a phosphate-rich overflow concentrate and an underliow stream;

(2) Subjecting the underflow from (l) to froth flotation in the presence of a cationic iiotationreagent to provide a phosphate-containing underflow concentrate :andy anoverow discard tail',` and (3) subjectingY the pnderow concentrate from (2) to gravity separation to provide` a phosphate-rich gravity` concentrate product.

In va preferred embodiment of. thevinvention, the phosphate-rich concentrate from the anionic flotation is subjected to further froth flotation in the presence of a cat-\ ionic reagent: to provide a. phosphate-rich underflow concentrate product and an. overflow silica. tail.

The process of. this invention provides asigniiicant recovery. of phosphate materials and may reduce the amount of ore to bev processed by gravity separation as compared to standard prior art. processes wherein phosphate tores are sized to obtain a coarse fraction which isy subjected to. gravity separationandfa fine. fraction which is subjected to iiotation. Moreover, the process of this invention eliminatesy the necessity of sizing the entire groundore.

Whereas conventional commercial processes recover from 85 to 90% of the phosphate values from `a phosphate ore originally containing -35 to 40% phosphate values, this invention permits recoveries of 90% to 95% of the phosphate values present. Accordingly, as compared to such process, this invention provides a simpliiied process which increases phosphate recovery.

This invention is generically applicable, without limitation, to phosphate ores amenable to wet concentration. Specific -ores contemplated include Florida pebble phosphate, the various Tennessee phosphates, hard rock phosphates indigenous to the Western United States, yand the various foreign phosphate ores such as Moroccan phosphates.

The phosphate ore to be treated in accordance with the process of this invention is preliminarily ground employing standard grinding apparatus known to the art to a mesh size generally of about '10, preferably about -12 mesh and deslimed to provide a mesh range of about or l2 to about +150 or 200 mesh. Grinding the ore to this stated mesh size generally is sufficient to liberate the phosphate values of the ore and to permit the ore effectively to be processed by this invention.

The ground ore then is reagentized employing any of the standard anionic or negative ion ilotation agents known to the art. The particular anionic reagent utilized in the preliminary froth flotation of the phosphate ores does not constitute an essential -feature of this invention which is operable with and contemplates all such reagents. Representative conventional anionic reagents comprise fatty acids or fatty acid soaps, particularly mixed fatty acids or soaps thereof; fatty acids derived from natural sources such as tal-l oil soaps and iloating soap; fatty acids or soaps of acids derived from animal and vegetable fats; esters of inorganic acids with high molecular weight alcohols; and the like. Conventionally, such anionic reagents are applied in solution or in a dispersion in a carrier medium such as a hydrocarbon oil, normally kerosene or fuel oil. One widely used speciiic reagent combination comprises about one to about three parts tall oil, from about two to about four parts kerosene, and from about two to about four parts Bunker C fuel oil.

The reagentized ore is subjected to froth flotation again employing any of the standard flotation equipment known to the art. The flotation is effective to remove in the overflow a substantial amount of the phosphate values of the ore together with some of the fine-r silica particles. The underflow wi-ll contain a substantial portion of silica and also will contain phosphate values, particularly in the form of coarser phosphate particles.

In accordance with the preferred embodiment of this invention, the anionic overilow concentrate is subjected to a further flotation in the presence of a cationic flotation reagent.

The anionic reagents advantageously are removed from the phosphate-rich over-flow concentrate employing such standard prior art means as scrubbing with Water or, more desirably, with a mineral acid such as sulfuric acid, hydrochloric acid and the like. In conformance with recognized procedures, the anionic concentration slurry may be partially tdewatered in order to permit a more eilicient removal of the reagent. Following the removal of the anionic reagent, the phosphate-rich concentrate is reagentized with a cationic reagent. While removal of the anionic reagent may improve the efficiency of subsequent processing, it is not critical to the operability of the process. Signicant phosphate recovery can be achieved Without removing the anionic reagent.

Again, this invention generically embraces the cationic or positive ion flotation reagents known to the art. Such reagents include, inter alia, the higher aliphatic amines and their salts with water-soluble acids; the ester of amino 'alcohols with high molecular weight fatty acids and their salts with `water-soluble acids; the higher alkyl- O-substituted isoureas and their salts with water-soluble acids; the higher aliphatic quaternary ammonium bases and their salts with water-soluble acids; the higher alkyl pyridinium water-soluble acids; the higher alkyl quinolinium salts of water-soluble acids and the like.

The phosphate-rich overflow from the iirst flotation, now reagentized with a cationic reagent, is subjected to a second `froth flotation. The ilotation removes predominantly the liner silica particles which were collected in the overflow concentrate of the anionic llotation and the overflow silica tail, substantially free of phosphate values, may be discarded, or if desired, processed further for other purposes.

The underllow stream lfrom the anionic froth flotation also desirably is de-reagentized and then reagentized with a cationic reagent and subjected to froth flotation. The flotation provides a phosphate-containing underllow which contains both phosphate and silica and particular-ly coarse phosphate particles and coarse silica. The overflow silica tail is substantiallyfree of phosphate.

The phosphate-containing underow finally is subjected to gravity separation to provide a second phosphate-rich concentrate product. The gravity separation may be carried out employing any of the means known to the art including, without limitation, spirals, tables, belts and the like. Spirals, for example, Humphrey spirals, are found to be particularly appropriate for the gravity separation of phosphate-rich concentrates. In conformance with recognized practice, the ore may be reagentized before being subjected to the gravity separation.

While each yflotation above described has been referred to as if conducted in a single flotation unit, it will be apparent that a battery of 'units in parallel or in series may (be employed for each ilotation stage. Thus, for example, the preliminary anionic ilotation can #be accomplished in a battery of rougher anionic ilotation cells to produce a phosphate-rich lrougher overilow which in turn is processed further in anionic cleaner -otation cells to produce a phosphate-rich overilow concentrate. Such expedient is particularly appropriate in the event that the phosphate concentrate is not to lbe subjected 'to further upgrading by cationic ilotation. Similarly, the cationic flotation stages reierred to above may consist of a battery of rougher cells employed in conjunction with a secondary battery of cleaner cells.

'Ilhe control of flotation air rates, fthe solids content of the slurry in the flotation unit and similar process conditions are within the skill of the routineer. Tests indicate that the anionic reagent can most appropriately be employed in amounts .of at least about .2 pound per ton, and the anionic underflow most appropriately may be conditioned with at least about 0.8 pound per ton of a cationic reagent. These reagents may he employed in amounts up to 10 pounds per ton or more, if desired. The use of large quantities of reagent, off course, tends to effect adversely the economics of the process.

lIlhe method of this invention is demonstrated llows'heets in fthe attached drawings.

lFIGURE. i1 represents a `diagrammatic ilowsheet of the method of this invention.

FIGURE 2 represents one preferred ilowsheet for the method of this invention.

Referring to FIGURE 1, the ideslimed, unsized ore (-114 +150) :from feed hin .1 is mixed with a flotation agent composition such as tall oil and delivered to flotation :unit 2. Froth ilotation provides an yoverflow phosphate-rich fraction which is tde-watered at rie-watering station 3 to provide a high-solids slurry, eig. 75% solids. 'Ilhe tde-watered concentrate then is conveyed to mixing station 4 where sulfuric acid is added to remove the anionic flotation reagents. The concentrate then is washed to neutrality at washing station 5 and conveyed to llotation unit `6 wherein it is iloated with a cationic flotation agent such as a long-chain aliphatic amine. Flotation funit =6 yields an underllow phosphate product and an overflow silica tail. The underilow from the lby the ilotation unit 2 is rde-watered at station 7, mixed with a mineral acid such as sulfuric acid at stationV 8- t-o remove the anionic reagent and washed at station 9 to neutrality. Since the `underiow stream from flotation unit 2 conrtains predominantly nnreagentized material, stations 7, 8i

and 9 may be eliminated if desired. The underflow from flotation unit 2 is fed to dictation unit 10 wherein it is subjected to froth ilotation in the presence of a cationic reagent, such as a long-chain aliphatic amine. Flotation unit 10 provides an overflow silica tail and an underflow product containing the ooarser phosphate and silica values of .the ore. This stream is subjected to gravity separation, such as spiraling, at station 11 to provide a `iinal phosphate concentrate and a silica tail. lFrom the earlier description of the process it will be apparent that this invention also contempla-tes a process wherein a first phosphate product is removed as the overow from flotation -unit 2 and reagent removal stations 3, 4, 5 and ilotation -unit 6 are not employed.

rFIGURE 2 represents one preferred embodiment of the process of this invention. The unsized de-sl-imed phosphate ore trom the deed bin 21 is reagentized with an anionic reagent such as tall oil and subjected Ito a rougher flotation operation in iiotation unit 22. 'Ilhe phosphaterich overflow from unit 22 is subjected to a cleaner flotation at flotation unit 23 |to provide aphosphate-rich overflow and a silica-containing underflow. The silica-containing nnderflow is subjected to a scavenger iiotation in otat-ion unit 24 again to provide a phosphate-rich overow and a silica-containing underow. The overflows from flotation alnits 23 and 24 are combined and dewatered, scrubbed with a mineral acid and washed at stations 25, 26 and 27. The concentrate then is subjected to otation .in the presence of a cationic reagent at flotation unit 28 to provide an lover-flow silica tail and an under-How final phosphate concentrate. The underiiow from rougher Iotation unit 22 is combined with the underow from scavenger ilotation unit 24 an-d the combined runderows are subjected to rde-watering, scnurbbing with a mineral acid and washing at stations 29,y 30 and 31. 'Phe combined nnderows then are subjected to flotation in the presence of a cationic lflotation reagent such as a long-chain aliphatic amine at iiotation unit 32. Flotation unit 32 provides an overflow silica tail and runderow stream containing the coarser particles of phosphate and silica. The .underow is subjected to gravity separation, as for example in spirals, at station 33 -to provide a second phosphate concentrate and a silica tail.

'Iihe following examples are included in order more fully to :describe the process of this invention. These examples are included for illustrative purposes `only and in no way are intended to limit the scope of this invention.

EXAMPLE I Approximately 70() t./h. (tons per hour) `of phosphate or (37.5% BPL), ground and washed to about -16 +150, is conditioned with 1.5 lb./ton1of anionic reagent (1:1:2-tall oil:kerosene:Bunker C `fuel oil) and subjected to a rougher llotation to yield an overflow of 372 t./h. (55% BPL) and an underilow of 328 t./h. (8% BPL).

The overow is subjected .to a cleaner -flotation to yield a cleaner overflow of 293 t./h. (63% BPL) and a cleaner underflow of 79 t./h. (25% BPL).

'Phe combined nnderows from the anionic rougher and cleaner iioats -is conditioned with l lb./ ton of a mixture of long-chain amines with added kerosene and subjected to flotation to yield an underflow of 84 |t./h. (45% BPL) and an overow of 323 t./h. (2.5% BPL).

Finally, the 84 t./h. cationic nnderiiow `is subjected to gravity separation in a spiral section to provide a concentrate of 47 t./h. (74.4% BPL) and a tail of 37 t./h. (9% BP-L).

The total BPL recovery of the above process is 94.3%.

6 A standard process utilizing gravit-y separation for mesh ore and an analogous method to the above to process -35 mesh Aore recovers only about 88% of-'the BPL of the ore.

EXAMPLE II ln order to `determine the characteristics of the anionic float and of the cationic float of the anionic underflow,-

without dereagentizing phosphate ore ground andv washed to -16 L-j-150 mesh size and analyzing 371.5% BPL wlas subjected to anionic rougher iiotationi andr the overilow was subjected to a cleaner notation. The combined underow from the rougher and cleaner -oats then-.Was subjected to a cationic ilotation.

The ore wlas fed to the process at a rate of 02.15` ton per hour. Five cells were employed for the rougher float, 3 cells for the cleaner tloat, `and 4 cells ory the cationic float. For the anionic float, the `ore was reagentized with 1.47 pounds/ton ofl tall.' oil in an emulsion (1:1:2-tall oil:kerosene:Bunker C iuel oil), andr0.45 l-b./ton of NaOH. For the cationic oat, ore wasreagentized with 1.02 lbs/Iton of mixed long-chain amines.

The analyses of the process streams are set forth in Table 1 below.

`Each of the streams was also screened at 35 mesh. The screen analysis of the streams is reected by Table 2.

Table 2 +35 mesh -35 mesh Stream Weight BPL Weight BPL percent percent percent percent Anionic cleaner oat 18.1 78. 7 81. 94 67. 5 Cationic underflow- 51. 0 54. 6 49. 0v 39. 3 CatiOnic fl0at 7. 7 1. 9 92. 3 2. 2

Composite 21 55.0 79. 0 34. 3

The data `of Table 2 demonstrate that .the -l-35 mesh fraction constituted about 51% of the cation-icvunderow as contrasted to only 21% of the feed. The dataalso demonstrate that predominately finer material was removed by both the anionic and the cationic iloat.

While the method has been described as a continuous process, it will be apparent that it also can be practiced as -a biatch process. Since this and other modications will be apparent .to one skilled in the art, it is intended that this invention be limited only by the scope of the appended claims.

I claim:

1. The method of heneciating unsized phosphate ore which comprises:

(1) subjecting an unsized liberated desli-med phosphate ore fraction containing particles of -a mesh 4size of `from about 10 mesh to about 200 mesh to froth fiotation in the presence of an anionic flotation reagent to provide a phosphate-rich overow concentrate and an unde-row stream;

(2) subjecting the underflow from (1) to fnoth otlation in the presence of ra cationic otation reagent to provide a phosphate-containing underflow concentrate and an overow discard tail; and

(3) subjecting the underflow `concentrate from (2) to gravity separation to provide a phosphate-rich gravity concentrate product.

2. The method of claim 1 wherein the anionic reagent is selected from the group consisting of fatty acids and fatty acid soaps.

3. The method of claim 1 wherein the cationic reagent is an aliphatic amine.

4. The method of beneticiiating unsized phosphate ore which comprises:

1(1) subjecting an unsized liberated deslimed phosphate ore fraction containing particles of a mesh size of from about 10 mesh to about 200 mesh to froth flotation in the presence of an anionic flotation reagent to provide a phosphate-rich overow concentrate and an underow stream;

(2) subjecting the phosphate rich overflow from (1) to froth otation in the presence of a `cationic flotation reagent to provide a phosphate-rich underow concentrate and an overow silica tail;

(3) subjecting the underow from (1) to froth otation in the presence of a cationic iiotation reaagent to provide a phosphate-containing underilow concentrate and an overow discard t-ail; and

(4) subjecting the underflow concentrate from (3) to gravity separation to provide a phosphate-rich gravity concentrate product.

5. The method of claim 4 whe-rein the anionic reagent is selected fnom the group consisting of fatty acids and fatty acid soaps.

6. The method of claim 4 wherein the cationic reagent is an aliphatic amine.

7. The method of beneciating an unsized phosphate ore which comprises:

(1) subjecting an unsized liberated deslimed phosphate ore fraction containing particles of a mesh size of from about 10 mesh to about 200 mesh to fnoth otation in the presence of an .anionic otation reagent to provide a phosphate-rich overow concentrate and an underow streamf Y (2) subjecting the phosphate-rich overow from 1) to a cleaner froth otation to provide a phosphaterich cleaner overow and an underilow;

(3) subjecting the phosphate-rich overilow from (2) to froth otation 4in the presence of a cationic flotation reagent to provide -a phosphate-rich underflow and an overiow silica tail;

(4) subjecting the underilows from 1) and (2) to froth otation in the presence of a cationic tlotation reagent to provide a phosphate-rich underflow and an overflow silica tail; and

(5) subjecting the underflow from (4) to gravity separation to provide a phosphate-rich concentrate and a silica tail.

8. The method of claim 7 wherein the anionic reagent is selected from the group consisting of fatty acids and fatty acid soaps and the cationic reagent is an aliphatic amine.

9. The method of beneficiating unsized phosphate ore which comprises:

(l) subjecting an unsized liberated deslimed phosphate ore fraction containing particles of a mesh size of from about 10 mesh to about 200 mesh to froth ilotation in the presence of an anionic otation reagent to provide a phosphate-rich overflow concentrate and an underliow stream;

(2) subjecting the phosphate-rich overilow from (l) to a cleaner froth flotation to provide a phosphaterich cleaner over-How and Ian underflow;

(3) subjecting the underow from (2) to a scavenger froth otation to provide a phosphate-rich scavenger overow and an underow;

(4) subjecting the phosphate-rich overows from (2) and (3) to froth otation in the presence of a cationic flotation reagent to provide a phosphate-rich underflow and an overflow silica tail;

I(5) subjecting 'the underows from (1) and (3) to froth flotation in the presence of a cationic flotation reagent to provide a phosphate-rich underow and an overow silica tail; 'and (6) subjecting the underilow from (5 to gravity separation to provide a phosphate-rich concentrate and a silica tail.

110. The method of claim 9 wherein the anionic reagent is selected from the group consisting of fatty racids and fatty acid soaps and the cationic reagent is an aliphatic amine.

11. The method of claim 1 wherein said unsized liberated deslimed phosphate ore fraction contains particles of a mesh size of from about 12 mesh to iabout 150 mesh.

12. The method of claim 4 wherein said unsized liberated deslimed phosphate ore fraction contains particles of a mesh size of from about 12 mesh to about 150 mesh.

13. The method of claim 7 wherein said unsized liberated deslimed phosphate ore fraction contains particles of a mesh size of from about 12 mesh to about 150 mesh.

14. The method of claim 9 wherein said unsized liberated deslimed phosphate ore fraction contains particles of a mesh size of about 12 mesh to about 150 mesh.

References Cited in the le of this patent UNITED STATES PATENTS 2,553,905 Evan-s May 22, 1951 2,668,617 Houston Feb. 9, 1954 2,750,036 Hunter June 12, 1956 2,811,254 McGarry Oct. 29, 1957 2,914,173 Le Baron Nov. 24, 1959 2,922,522 Penske Ilan. 26, 1960 2,967,615 Goin Jan. 10, 1961 

1. THE METHOD OF BENEFICIATING UNSIZED PHOSPHATE ORE WHICH COMPRISES: (1) SUBJECTING AN UNSIZED LIBERATED DESLIMED PHOSPHATE ORE FRACTION CONTAINING PARTICLES OF A MESH SIZE OF FROM ABOUT 10 MESH TO ABOUT 200 MESH TO FORTH FLOTATION IN THE PRESENCE OF AN ANIONIC FLOTATION REAGENT TO PROVIDE A PHOSPHATE-RICH OVERFLOW CONCENTRATE AND AN UNDERFLOW STREAM; (2) SUBJECTING THE UNDERFLOW FROM (1) TO FROTH FLOTATION IN THE PRESENCE OF A CATIONIC FLOTATION REAGENT TO PROVIDE A PHOSPHATE-CONTAINING UNDERFLOW CONCENTRATE AND AN OVERFLOW DISCARD TAIL; AND 